A colony of primates, Macaca fascicularis, infected with Strep. mutans and being fed a cariogenic diet, is being used to develop a vaccine against dental caries. Animals vaccinated with glucosyl transferase preparations continue to show protection and to harbor serum antibodies which react with GTF and other potential immunogens. A group of recently imported young animals was found to have high levels of serum antibody reactive with S. mutans although S. mutans was not detected in any animals using either FA or cultural techniques. The organism believed responsible for inducing antibody reactive with S. mutans has been isolated.